Where do the constraints come from?
•Bandwidth (bits per second) over a link is often unknown and certainly time
varying
•Packet switched networks operate with unknown and time varying delays
and packet losses
•Device capability varies enormously
Movie Download
Download speed proportional to size of file. Large
files imply less movies on your device, and long
download times.
Files encoded at a high bits/pixel mean that a lot
of data has to be read from storage before
decoding. Your storage access speed might not
be fast enough to keep up with real time playback.
Long download times and lots of storage access =
low battery life.
Streaming Movies
Files encoded at a high bits/pixel (high compression
rate) mean that a lot of data has to be streamed before
you can decode a picture. Hence
-- Your decoder buffers might “overflow” before you can
decode a picture. So you end up skipping frames.
-- Or your decoder/cpu might not be fast enough to
decode the data in time. So you end up skipping
frames.
-- Or your bandwidth might be too low to keep up with
your decoder (buffer underflow) and you get the
YouTube “spinny wheel”.
Files encoded at low bits/pel (low compression rate) can
imply bad looking pictures.